This invention relates to the production of glass fibers, e.g., fibers made by melting particulate batch ingredients or minerals, including basalt and the like, and, more particularly, to an electric furnace which uses an arc and/or electrodes for causing electrical current to flow through the batch for melting such batch materials.
The copending patent application of Charles S. Dunn, Ser. No. 342,852 which has been assigned to a common assignee, discloses an arc glass-melting furnace which utilizes a plurality of electrodes positioned in the bottom of the furnace to complete the arc circuit. It has been found that in certain instances a majority of the current is conducted through the molten glass to one electrode rather than being split equally between the electrodes. This problem is created by the negative temperature coefficient of glass which causes a decrease in the resistance of the body of molten glass as the temperature is increased. As a result thereof, the conductivity of the glass increases with the increasing temperature to produce an unlimited or runaway local heating condition. Accordingly, when more of the current from the arc electrode flows to one of the electrodes than the other, the increased current flow will cause a temperature rise which, in turn, causes a reduction of the effective resistance path to that electrode because of the negative temperature coefficient, thereby causing even more current to flow to that electrode with the result that a smaller portion flows to the other electrode. This unbalance can result in devitrification of the glass in the cooler portions of the furnace through which the lesser amount of current is flowing and damage to the furnace structure in the portion that is undergoing the runaway heating condition.
Therefore, it is an object of the present invention to provide an arc glass-melting furnace that balances the current flowing from the arc electrode through the molten glass, thereby preventing devitrification and insuring a uniform temperature throughout the molten glass.
It is also an object of the present invention to provide an electrically heated glass-melting furnace which uses only resistive heating produced by equalized current flow through individual electrodes disposed within the glass to produce uniform temperatures throughout the glass sufficient to permit glass fibers to be drawn directly from the furnace without further processing.